The human ear includes three parts, identified generally as the outer ear, the middle ear and the inner ear. The middle ear includes three small bones. The malleus, or hammer, connects to the tympanic membrane, also known as the eardrum, of the outer ear. The malleus is in turn connected to the incus, or anvil. The incus is connected to the stapes, or stirrup. These three small bones are also commonly referred to as ossicles, or collectively as the ossicular chain. The three bones operate as a lever and piston system that amplifies the force of sound vibrations. The stapes is in turn connected to the oval window, or stapes footplate, of the inner ear. The stapes applies pressure at the stapes footplate, which is transmitted to parts of the cochlea of the inner ear.
Due to disease, trauma or congenital malformation, the ossicles of the middle ear are sometimes damaged. One common cause is otosclerosis, which may result in fixation of the stapes. This may lessen or eliminate vibration of the stapes, resulting in a conductive hearing loss. As a result of otosclerosis, and other conditions, approximately 30,000 patients in the U.S. each year undergo a stapedectomy, which is a surgical procedure involving the removal of one of the bones of the middle ear responsible for transmission of vibration from the eardrum to the cochlea. Often, this procedure involves the replacement of the stapes bone with a prosthesis.
An exemplary technique for replacing the stapes bone with a prosthesis is shown in FIGS. 1A-1C, with a corresponding stapes prosthesis shown in FIG. 2. The stapes bone 110 is typically reconstructed by creating an opening 120 into the stapes footplate 130 by removal of a portion or all of the damaged stapes 110. The stapes prosthesis 200 is then placed into the newly created opening 120. The prosthesis 200 is attached to a remaining middle ear ossicle 140, referred to as the anchoring ossicle, so that sound vibrations are transmitted from the ear drum to the stapes footplate opening.
Designs for stapes prostheses vary somewhat, but in general, as illustrated in FIG. 2, they include a thin wire 210. The thin wire 210 is fitted on one end of a piston element 220, often constructed from a plastic such as Teflon. The exposed end of the wire 210 is crimped to the incus bone, and the piston end 220 is positioned within the hole 120 created in the stapes footplate 130, within the inner ear. The prosthesis 200 effectively mimics the function of the original stapes, carrying vibrations from the incus to the cochlea.
For approximately 6-10% of patients with a stapes prosthesis, otosclerosis is a continuing problem which may lead to failure of the prosthesis and the need for additional surgery. Drug compounds, such as bisphosphonates, help to prevent this continued bone resorption, but have side effects that make site-specific delivery of the drug desirable compared to systemic delivery.
The use of polymer-loaded matrices for delivery of drug to the middle ear has been previously described. However, such devices are limited to drug delivery and, as such, a separate additional implanted device, such as a stapes prosthesis, is still required to directly relieve the problem causing the impaired hearing.
In addition, current drug delivery devices are often difficult to place within the middle ear, especially if the device is to be large enough to hold a useful amount of drug while also allowing delivery of a drug directly into the cochlea. This may limit the allowable room for placement of an additional prosthetic device, or other treatment device, within the ear.
Other methods may also be utilized for delivery of a drug to the middle ear. For example, direct injection of drugs may be possible, although this may often be undesirable as it would require repeated invasive treatments by a physician. Other devices, such as polymeric drug carriers or microfluidic pumps, may also be implanted in a patient, allowing for the delivery of a drug to either the middle or inner ear. Again, however, a separate, additional, implanted device, such as a stapes prosthesis, would still be required.